A bathymetric map uses contour lines to depict the submerged terrain of a waterbody in the same way that a topographic map depicts the terrain of a landscape. Bathymetric maps are important for water quality monitoring because monitoring is generally conducted at the location in the lake where the water is deepest, dubbed the “deep spot”. Lake water first becomes anoxic at the bottom of the deepest point in the lake and therefore internal loading also begins at this point (visit The Basics of Limnology page for more information about this process).  Monitoring is conducted at the deepest spot in the lake. Monitoring may be conducting at multiple locations on the lake if there is more than one recession. Therefore, it is necessary to know the water depth throughout the lake to determine where to collect data.

Bathymetric maps are also important for fishermen and boaters to know where the shallow and deep spots are located in the lake. 

We create bathymetric maps by driving uniform transects across the lake and using a depth sounder to record the depth of the water. Old bathymetric maps may not be accurate because the lake bottom fills in over time, causing the lake to become shallower than depicted in the map.